A couple of thoughts come to mind. It may be leaning towards the sun. Hibiscus 'Blue Bird' prefers full sun. Another possibility is it may have been planted at a bit of an angle or was even that way in it's original container, and has continued to lean with the added weight of the flowers.
From this site which might help you:
Late winter or early spring pruning will keep it from getting rangy, & encourage a central few branches to bulk up with nice woody form. A hard pruning in late winter will result in fewer but much larger five-inch-wide flowers, whereas a moderate pruning results in smaller flowers but in greater numbers.
Because 'Blue Bird' is comparatively slow in its growth rate, it remains compact without as much pruning as most varieties of H. syriacus, but failure to prune annually results in an increasingly leggy shrub that blooms less & less well, because it flowers exclusively on new wood. As a conservative average, a full one-third of the previous year's growth should be trimmed out each January or March well before new growth begins, but more certainly can be trimmed.